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[216.228.112.22]) by smtp.gmail.com with ESMTPSA id a12sm36918995pgq.21.2019.04.29.18.57.02 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Apr 2019 18:57:03 -0700 (PDT) From: Nicolin Chen To: hch@lst.de, robin.murphy@arm.com, m.szyprowski@samsung.com Cc: vdumpa@nvidia.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, chris@zankel.net, jcmvbkbc@gmail.com, joro@8bytes.org, dwmw2@infradead.org, tony@atomide.com, akpm@linux-foundation.org, sfr@canb.auug.org.au, treding@nvidia.com, keescook@chromium.org, iamjoonsoo.kim@lge.com, wsa+renesas@sang-engineering.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-xtensa@linux-xtensa.org, iommu@lists.linux-foundation.org Subject: [RFC/RFT PATCH 2/2] dma-contiguous: Use fallback alloc_pages for single pages Date: Mon, 29 Apr 2019 18:55:21 -0700 Message-Id: <20190430015521.27734-3-nicoleotsuka@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190430015521.27734-1-nicoleotsuka@gmail.com> References: <20190430015521.27734-1-nicoleotsuka@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The addresses within a single page are always contiguous, so it's not so necessary to always allocate one single page from CMA area. Since the CMA area has a limited predefined size of space, it may run out of space in heavy use cases, where there might be quite a lot CMA pages being allocated for single pages. However, there is also a concern that a device might care where a page comes from -- it might expect the page from CMA area and act differently if the page doesn't. This patch tries to use the fallback alloc_pages path, instead of one-page size allocations from the global CMA area in case that a device does not have its own CMA area. This'd save resources from the CMA global area for more CMA allocations, and also reduce CMA fragmentations resulted from trivial allocations. Signed-off-by: Nicolin Chen --- kernel/dma/contiguous.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c index afe5a673668e..71aba1551275 100644 --- a/kernel/dma/contiguous.c +++ b/kernel/dma/contiguous.c @@ -186,14 +186,23 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base, * This function allocates contiguous memory buffer for specified device. It * first tries to use device specific contiguous memory area if available or * the default global one, then tries a fallback allocation of normal pages. + * + * Note that it byapss one-page size of allocations from the global area as + * the addresses within one page are always contiguous, so there is no need + * to waste CMA pages for that kind; it also helps reduce fragmentations. */ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp) { int node = dev ? dev_to_node(dev) : NUMA_NO_NODE; size_t count = PAGE_ALIGN(size) >> PAGE_SHIFT; size_t align = get_order(PAGE_ALIGN(size)); - struct cma *cma = dev_get_cma_area(dev); struct page *page = NULL; + struct cma *cma = NULL; + + if (dev && dev->cma_area) + cma = dev->cma_area; + else if (count > 1) + cma = dma_contiguous_default_area; /* CMA can be used only in the context which permits sleeping */ if (cma && gfpflags_allow_blocking(gfp)) { -- 2.17.1